Many medical complications are created by the total or even partial blockage of blood vessels of the body. The primary cause of these complications is, of course, the reduction or cessation of blood flow through the blocked vessels to the particular biological tissue which is serviced by the vessel. Most commonly, a blockage, or stenosis, is formed in an artery as a result of plaque build-up in the artery. Further, it is not uncommon for several stenoses to occur sequentially in a single artery or to develop near one another in branches of a common central artery.
Several methods, or procedures, have been developed in the medical field for the purpose of removing or clearing stenoses from the vessels of patients. One well known procedure for accomplishing this is an angioplasty procedure such as is disclosed in U.S. Pat. No. Re. 33,561 which issued to Levy for an invention entitled "BALLOON AND MANUFACTURE THEREOF." Basically, in an angioplasty procedure, a deflated dilatation balloon is inserted into the vessel and is placed across the stenosis. Once the balloon is properly positioned, it is inflated to dilate the artery and thereby clear the stenosis. Another, more recently developed procedure for clearing a stenosis, is an atherectomy procedure.
The essential aspects of an atherectomy procedure are set forth in U.S. Pat. No. 4,895,166 which issued to Farr et al. for an invention entitled "ROTATABLE CUTTER FOR THE LUMEN OF A BLOOD VESSEL" and which is assigned to the same assignee as the present invention. As disclosed by Farr et al., in an atherectomy procedure, the stenotic material is actually cut and removed from the artery.
Both the angioplasty procedure and the atherectomy procedure are typically accomplished indirectly wherein access to the stenosis is achieved through a peripheral artery. These procedures are in contrast to other known procedures used to clear arteries, such as a by-pass surgery, where direct access to the stenosis is achieved by entering the artery at or near the site of the stenosis. Despite their differences, the ultimate objective of all these procedures is to remove or alleviate the stenosis which is restricting blood flow through the artery.
Recent studies have indicated that for procedures wherein a stenosis is to be dilated, such as for an angioplasty procedure, the efficacy of the dilatation is enhanced by first incising the material which is creating the stenosis. With this knowledge, several devices for clearing blocked arteries have been proposed. For example, U.S. Pat. No. 4,273,130 which issued to Lary for an invention entitled "CORONARY CUTTING AND DILATING INSTRUMENT" discloses a surgical instrument which both incises and dilates a stenosis. As another example, U.S. Pat. No. 5,209,799 which issued to Vigil for an invention entitled "METHOD FOR MANUFACTURING A FOLDING BALLOON CATHETER" discloses a folding angioplasty balloon with attached cutting blades.
Angioplasty, atherectomy and by-pass surgery procedures, as discussed above, have all been found to be effective procedures for dilation and removal of occluding stenoses. In some cases, however, these procedures have been found to be less effective. For example, it happens that the coronary arteries where many stenoses occur have a tapering geometry with the arteries generally having an internal diameter which is greatest near the heart and which decreases at distances farther from the heart. When a stenosis accumulates in a tapering artery, such as a coronary artery, the stenosis will itself have a tapering geometry. If the stenosis is relatively long, the tapering effect can be quite pronounced. As a result, many of the traditional methods of angioplasty and atherectomy devices may be ineffective, or even harmful. For example, if a traditional angioplasty device is used in a long stenotic segment in a tapering artery, it may over dilate the narrowest part of the stenosis while under dilating the widest part of the stenosis. As a result, the procedure fails to fully clear the stenosis and, possibly, weakens the involved vessel. Similarly, if an incising or atherectomy procedure is to be used in a long stenotic segment in a tapering artery, the cutting diameter of the device will necessarily have to be chosen to protect the narrowest part of the involved vessel, lessening the effectiveness of the procedure on the vessel's widest part.
Even in cases where the stenotic segments are relatively short, the tapering geometry of many vessels may be problematic if a sequence of such segments must be cleared. More specifically, it may be appreciated that where sequences of stenotic segments are involved, and the segments are positioned within a single tapering vessel, treatment may be problematic if the apparatus employed cannot adapt to the decreasing internal diameter of each subsequent stenotic segment.
In light of the above, it is an object of the present invention to provide a device and method for incising and dilating a stenosis in a vessel of a patient which is particularly efficacious for removal of relatively long stenotic blockages in tapering vessels. Another object of the present invention is to provide a device for incising and dilating a stenosis in a vessel of a patient which can be reconfigured in-situ to allow treatment of a sequence of stenotic segments, each positioned further into a tapered vessel. Yet another object of the present invention is to provide a device for incising and dilating a stenosis in a vessel of a patient which is relatively simple to manufacture, is easy to use, and is comparatively cost effective.